Which of these numbers is prime? ${54,\ 75,\ 83,\ 87,\ 95}$
Answer: A prime number has exactly two factors: 1 and itself. The factors of 54 are 1, 2, 3, 6, 9, 18, 27, and 54. The factors of 75 are 1, 3, 5, 15, 25, and 75. The factors of 83 are 1 and 83. The factors of 87 are 1, 3, 29, and 87. The factors of 95 are 1, 5, 19, and 95. Thus, 83 is a prime number.